The Singaporean military is arguably the most technologically advanced in Southeast Asia. It comprises the Army, Navy, and Air Force. It is seen as the guarantor of the country's independence. The nation's philosophy of defence is one of diplomacy and deterrence. This principle translates into the culture, involving all citizens in the country's defence. The government spends 4.9% of the country's GDP on the military and one out of every four dollars of government spending is spent on defence.

On independence, Singapore had two infantry regiments commanded by British officers. This force was considered too small to provide effective security to the new country, so the development of the military became a priority. Britain pulled its military out of Singapore in October 1971, leaving behind only a small British, Australian and New Zealand force as a token military presence. The last British soldier left Singapore in March 1976. New Zealand troops were the last to leave, in 1989.

A great deal of initial support came from Israel, a country that is not recognised by neighbouring Islamic Malaysia, Indonesia or Brunei. The main fear after independence was an invasion by Malaysia. Israel Defense Forces commanders were tasked with creating the Singapore Armed Forces from scratch, and Israeli instructors were brought in to train Singaporean soldiers. Military courses were conducted according to the Israel Defense Forces' format, and Singapore adopted a system of conscription and reserve service based on the Israeli model. Singapore still maintains strong security ties with Israel and is one of the biggest buyers of Israeli arms and weapons systems. The MATADOR is one example of recent Singapore-Israeli collaboration.

The SAF is being developed to respond to a wide range of issues, in both conventional and unconventional warfare. The Defence Science and Technology Agency is responsible for procuring resources for the military. The geographic restrictions of Singapore mean that the SAF must plan to fully repulse an attack, as they can not fall back and re-group. The small size of the population has also affected the way the SAF has been designed, with a small active force but a large number of reserves.

Singapore has conscription for all able-bodied males at age 18, except those with a criminal record or who can prove that their loss would bring hardship to their families. Males who have yet to complete pre-university education or are awarded the Public Service Commission scholarship can opt to defer their draft. Though not required to perform military service, the number of women in the SAF has been increasing: since 1989 they have been allowed to fill military vocations formerly reserved for men. Before induction into a specific branch of the armed forces, recruits undergo at least 9 weeks of basic military training.

Because of the scarcity of open land on the main island, training involving activities such as live firing and amphibious landings is often carried out on smaller islands, typically barred to civilian access. This also avoids risk to the main island and the city. However, large-scale drills are considered too dangerous to be performed in the area, and since 1975 have been performed in Taiwan. Training is also held in about a dozen other countries. In general, military exercises are held with foreign forces once or twice per week.

Due to airspace and land constraints, the Republic of Singapore Air Force (RSAF) maintains a number of overseas bases in Australia, the United States, and France. The RSAF's 130 Squadron is based in RAAF Base Pearce, Western Australia, and its 126 Squadron is based in the Oakey Army Aviation Centre, Queensland. The RSAF has one squadron – the 150 Squadron – based in Cazaux Air Base in southern France. The RSAF also has a few overseas detachments in the United States, in San Diego, California, Marana, Arizona, Grand Prairie, Texas and Luke Air Force Base, among others.

The SAF has sent forces to assist in operations outside the country in areas such as Iraq and Afghanistan, in both military and civilian roles. In the region, it has helped stabilise East Timor and has provided aid to Aceh in Indonesia following the 2004 Indian Ocean earthquake and tsunami. The SAF also helped in relief efforts during Hurricane Katrina. Singapore is part of the Five Power Defence Arrangements, a military alliance with Australia, Malaysia, New Zealand, and the United Kingdom.